In construction machinery and other vehicles serving as the work place of drivers and/or other operators the air conditioning has to be very efficient, especially during the warm season. Cooling units based on the use of halogenated hydrocarbons such as freon as the cooling agent, are today used in the majority of such work places. These units are often efficient and relatively compact in size, but they suffer from the severe drawback that this type of cooling agent is a danger to the environment, i.a. due to the unfavorourable effect on the ozon layer of the earth.
There is thus a great need of alternative cooling units using environment-positive cooling agents. A known alternative is to make use of the evaporation of water for cooling the supply air to the driving compartment in construction machinery, the air being passed through an evaporation block having an enlarged surface area and being charged with water, the water being evaporated in said block while cooling the air. Such surface-enlarged evaporation blocks are known per se, e.g. being formed by a lattice of moisture-resistent cardboard (e.g. CELDEK C-5090-15, available from Munthers Svenska Forsaljnings AB, Sollentuna, Sweden).
However, the known cooling units of this type have certain drawbacks and have only been used to a limited extent. As is obvious, they have a continuous demand of "cooling agent", i.e. of water to be evaporated, and the evaporation block normaly has to be kept supersaturated with water; in practice this means that excess water accumulates under the cooling unit. The previously known cooling devices have not solved the problem of handling the excess water in a satisfactory manner; this has i.a. resulted in a high water consumption, requiring oversized water tanks, and splashing of excess water into the driving compartment, especially when the vehicle slants when e.g. going downhill.